1
general::
1. Be in confinement for childbirth, as in She thought she'd be lying in by next week. This usage is probably dying out. The name of Boston's Lying-In Hospital was changed to Women's Hospital in the 1970s. [Mid-1400s] 2. Also, lie in one's hands or in one's power. Rest or depend on something or someone, as in The solution lies in research, or The decision lies in the President's hands, or It does not lie in my power to turn this situation around. [Mid-1300s] Also see LIE IN WAIT; LIE THROUGH ONE'S TEETH.
American Heritage Idioms
2
general::
Phrase(s): lie in
[for a woman] to lie in bed awaiting the birth of her child. • The child is due soon, and the mother is lying in at the present time. • She did not lie in at all. She worked right up to the onset of labor pains., Phrase(s): lie in something
to recline in something, such as a bed, a puddle, etc. • I found my wallet lying in a puddle. My money was soaked! • We found Jimmy lying in a pile of leaves, napping.
McGrawhill's American Idioms And Phrasal Verbs